In the fabrication of integrated circuitry, numerous devices are packed into a small area of a semiconductor substrate to create an integrated circuit. Many of the individual devices are electrically isolated from one another. Accordingly, electrical isolation is an integral part of semiconductor device design for preventing unwanted electrical coupling between adjacent components and devices.
As the size of integrated circuits is reduced, the devices that make up the circuits are positioned closer together. Conventional methods of isolating circuit components include trench isolation. Such occurs by etching trenches into a semiconductor substrate and filling the trenches with insulative material. As the density of components on the semiconductor substrate has increased, the widths of the trenches have decreased. Further, the depths of the trenches have tended to increase. One type of semiconductor substrate material within which isolation trenches are formed is crystalline silicon, and which may include other materials such as germanium and/or conductivity modifying dopants. A need remains for developing improved etching chemistries which enable trenches to be etched into silicon, for example in the fabrication of trench isolation.